Described below is a roll casting method,                wherein, in a mold region, which is delimited on at least one side by a first casting roll rotating around a horizontal first axis of rotation, molten metal is cast and a metal strand which is produced by the solidification of the molten metal is conveyed out of the mold region,        wherein a liquid coolant is applied to the surface of the first casting roll via a first cooling device by a number of first coolant applying devices,        wherein the cooling medium is fed to the first coolant applying devices via first coolant applying lines,        wherein the cooling medium is inert with respect to the molten metal, has a standard boiling point related to normal air pressure of below 20° C.—especially of below −20° C.—and has an operating temperature which lies at an operating boiling point or lower, wherein the operating boiling point relates to an operating pressure with which the cooling medium is applied.        
Such casting methods and the associated apparatus are generally known. Purely by way of example the reader is referred to JP 58 097 467 A.
When metals are cast to close to their final dimensions with a horizontal or vertical single-roll or two-roll casting machine or a strip casting system with casting thickness of below 15 mm, during the shaping of the metal strand which follows on from the casting, the influencing of profile and flatness of the end product is only still possible to a restricted extent. For this reason it is of advantage to already give the cast metal strand a suitable thickness profile or thickness contour during the casting process and in doing so avoid inter alia a tapering thickness if possible.
For influencing the cast profile with two-roll strip casting machines, use is made inter alia of the known fact that the cast strip thickness significantly depends on the flow of heat over the casting roll surface and the contact time. The two factors together determine how thick the strip shell can be at the location concerned. By variation of these variables over the casting roll width the thickness profile of the cast metal strand can thus be influenced to a significant extent.
The contour of the casting roll and the setting (position and/or downward pressure) of the casting roll itself have a further influence on the thickness profile of the strip. The contour of the casting roll in the casting gap is influenced by the thermal expansion and thus in turn by the local flow of heat.
The flow of heat over the casting roll surface is determined on one hand by the thermal transfer coefficient from the molten metal to the casting roll and to an even greater extent by the thermal transfer coefficient from the solidified strand shell to the casting roll. Furthermore the temperature difference between casting roll and strand shell or melt bath is decisive for the flow of heat.
The temperature of the casting roll is usually set in the related art by internal cooling—if necessary supplemented by external cooling. The contact time is determined by the rotational speed of the casting roll, the casting roll geometry and the mold level. When the melt bath surface is calm the contact time is constant in a first approximation over the width of the cast strand. Thus only the heat flow remains as a possible adjustment variable to influence the strand shell thickness and the roll geometry over the strand width.
It is already known that the heat flow over the strand width can be varied by influencing the thermal transition coefficient between the liquid metal or the strand shell and the casting roll. For example a gas with a high thermal conductivity can be dispensed segment-by-segment. Gas mixtures such as argon or nitrogen can also be used, of which components react chemically with the strip shell. In such cases the dispensing facility for the corresponding gas must be disposed in the vicinity of the triple point of molten metal, roll and gas space, in order to be able to bring the gas between the strand shell which forms and the casting roll. In this area of the roll casting system however space is very limited as a result of the arrangement of intermediate pans, molten metal distributors and sensors. This makes the construction and integration expensive, in many cases even impossible.
It is also known that the temperature of the cast roll can be influenced in a segmented manner by an additional liquid coolant applied externally to the cast roll. If water is to be used here it must be ensured however that no water or steam comes into contact with the molten metal. This is in particular because—depending on the metal used—this can result in quality problems or even serious disruptions (for example formation of hydrogen with the associated danger of explosion with non-ferrous metals). Suction and recovery devices taking up large volumes of space are therefore required in such cases.